A System-on-a-Chip (SoC) is an integrated circuit in which the components needed for a particular system to operate are included on a single semiconductor device. Today's SoC designs continue to grow in complexity and performance as technology processes provide greater and greater densities. With the development of new technologies and increased densities, the integrated circuit fabrication process also becomes more complex. One of the requirements for error-free chip fabrication is that a certain metal density threshold is maintained in all metal layers on the silicon die.
In order to maintain this metal density threshold, one of the final processes in integrated circuit layout design is a metal fill insertion process. In this step of the circuit layout design, a place and route tool looks for areas in any metal layer where the routing is not dense enough (i.e., does not meet the metal density threshold) and fills this area with metal fill (e.g., floating metal rectangles) to achieve the required metal density threshold. After the layout is filled with floating metal rectangles, the metal density is rechecked for compliance with the threshold requirement.